Abstract
Flow and transport processes in fractured systems are not yet fully understood, and it is challenging to determine the respective parameters experimentally. Studies on 10 samples of 2 different sandstones were used to evaluate the reproducibility of tracer tests and the calculation of hydraulic transport properties under identical boundary conditions. The transport parameters were determined using the advection–dispersion equation (ADE) and the continuous time random walk (CTRW) method. In addition, the fracture surface morphology and the effective fracture aperture width was quantified. The hydraulic parameters and their variations were studied for samples within one rock type and between both rock types to quantify the natural variability of transport parameters as well as their experimental reproducibility. Transport processes dominated by the influence of fracture surface morphology experienced a larger spread in the determined transport parameters between repeated measurements. Grain size, effective hydraulic aperture and dispersivity were identified as the most important parameters to evaluate this effect, as with increasing fracture aperture the effect of surface roughness vanishes and the experimental reproducibility increases. Increasing roughness is often associated with the larger effective hydraulic aperture canceling out the expected increased influence of the fracture surface morphology.
Highlights
Fractures are often the dominant fluid pathways in the subsurface due to the usually low intrinsic permeability of the reservoir rocks
Five drill cores were obtained from two different type of sandstones, fractured by the Brazilian test and subsequently investigated by tracer tests
When the influence of surface roughness on the flow and transport behavior is significant, there are variations in the transport behavior between repeated measurements, which are beyond experimental control
Summary
Fractures are often the dominant fluid pathways in the subsurface due to the usually low intrinsic permeability of the reservoir rocks. Detailed investigations of flow and transport processes in a single fracture contribute to the understanding of flow and solute transport in complex natural fractured systems [1,2,3,4,5]. Such investigations and the understanding of those processes are very important for practical applications, such as geothermal energy production [6] and the effective remediation of pollutants [7]. The occurrence of turbulent flow is mainly due to roughness [1,12], because surface roughness affects the permeability of a single fracture due to a heterogeneous aperture distribution. The surface morphology of a fracture can be determined in the Geosciences 2020, 10, 458; doi:10.3390/geosciences10110458 www.mdpi.com/journal/geosciences
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